Monitoring and display system for multi-stage compressor

ABSTRACT

A system is disclosed for sequentially monitoring and displaying the instantaneous value of a plurality of parameters associated with a motor driven device such as a multi-stage compressor. In addition to the basic functions of monitoring and displaying these values, the system performs a multitude of other functions such as: continuously comparing preselected ones of these parameters with pre-established reference signals to determine if these various parameters exceed predetermined safe limits; activating alarm devices should the particular parameters chosen exceed their pre-established limits; shutting down or otherwise controlling the device being monitored should the selected parameters exceed their predetermined levels so as to generate alarm signals; and storing the values of other preselected parameters such that these values can be subsequently displayed after the occurrence of an alarm situation. The system can be operated in a &#39;&#39;&#39;&#39;scan&#39;&#39;&#39;&#39; mode whereby the parameters are sequentially monitored, checked, and stored values updated at a preselected rate. Alternatively, an operator can select a particular station to be monitored in which case the instantaneous value of that particular parameter will continuously be displayed by the system. Regardless of whether the system is operated in the &#39;&#39;&#39;&#39;scan&#39;&#39;&#39;&#39; or &#39;&#39;&#39;&#39;hold&#39;&#39;&#39;&#39; mode, the occurrence of an alarm condition in any of the pre-established parameters will generate appropriate command signals to shut down or otherwise control the device being monitored; while at the same time, the value of the parameter which generated the alarm signal will be displayed on the apparatus.

United States Patent Zehr et al.

[54] MONITORING AND DISPLAY SYSTEM FOR MULTI-STAGE COMPRESSOR [72] Inventors: Richard M. Zehr, Tonawanda; James Mott, Butfalo; Lawrence Schlimgen, Tonawanda, all of NY.

[73] Assignee: Worthington Corporation, Harrison, NJ. [22] Filed: Sept. 24, 1969 [21 Appl. No.: 860,768

[52] U.S.Cl. ..340/l52R,235/l5l,340/413 Primary ExaminerDonald J. Yusko Att0rneyLerner, David & Littenberg DlSPLAY 22 51 3,665,399 1 May 23, 1972 [57] ABSTRACT pressor. In addition to the basic functions of monitoring and displaying these values, the system performs a multitude of other functions such as: continuously comparing preselected ones of these parameters with pre-established reference signals to determine if these various parameters exceed predetermined safe limits; activating alarm devices should the monitored should the selected parameters exceed their predetermined levels so as to generate alarm signals; and storing the values of other preselected parameters such that these values can be subsequently displayed after the occurrence of an alarm situation. The system can be operated in a *scan" mode whereby the parameters are sequentially monitored, checked, and stored values updated at a preselected rate.

Alternatively, an operator can select a particular station to be monitored in which case the instantaneous value of that particular parameter will continuously be displayed by the system. Regardless of whether the system is operated in the scan or hold" mode, the occurrence of an alarm condition in any of the pre-established parameters will generate appropriate command signals to shut down or otherwise control the device being monitored; while at the same time, the value of the parameter which generated the alarm signal will be displayed on the apparatus.

53 Claims, 17 Drawing Figures COMPARE SHIFT H8 SEQUENCE I08 I MEM- H LOGIC I06 '04 STORAGE 1 96 TRANS- mg i FER w I CONVERTER t SENSING U U w Patented May 23, 1972 15 Sheets-Sheet 5 XOMM.

RT H T M Jew E O m B MGM M 5mm M L D M NE R AC Q S *3. v: H E. mm mm W DH E iv R W 12 M L my JON 21 5 $1 (I wm Patented May 23, 1972 15 Sheets-Sheet 7 hwm mwm

+9. Sm m OTGE in m2] 20ml ONM m2: 20mm own 3 m m mom RICHARD M. ZEHR I JAMES MOTT LAWRENCE SCHLIMGEN INVENTORS B /2% Patented May 23, 1972 15 Sheets-Sheet 8 9 L 3 e h S 5 L 6 e h S no 1 Patented May 23, 1972 NWT RT HT 5% m fi ZMGW w, Mmmm L MH A S W E m m E 26 com R W A L Q8 ommfl|h M Patented May 23, 1972 13 Sheets-Sheet i1 whw ONF

RICHARD M ZEHR v JAMES MOTT LAWRENCE SCHLIMGEN Patented May 23, 1972 13 Sheets-Sheet 12 Nmm oww

RICHARD M. ZEHR JAMES MOTT LAWRENCE SCHLHVIGEN mwm BACKGROUND OF THE INVENTION This invention relates to monitoring and display apparatus and more particularly to a system which not only monitors and displays the value of a plurality of parameters associated with a particular device, but also relates to such a system which can performa multitude of other functions related to the satisfactory perfonnance of the particular device being monitored.

Monitoring and display problems are becoming increasingly more complex as the speed of operation and complexity of the device being monitored increases. For instance, in a multistage compressor for which the system of the instant invention was specifically designed, there are some 25 check points which must be continuously monitored to determine if the compressor is functioning properly. Should the parameters being monitored at preselected ones of these check points exceed predetermined safe limits, specific steps must be taken to either relieve the condition which caused the alarm situation or shut down the compressor completely.

One display system in common usage on such multi-stage compressors comprises nothing more than a plurality of dials responsive to appropriate transducers which sense temperature and pressure. This system requires the presence of one or more operators to continuously read these dials; compare their instantaneous indication with preestablished limits; and take necessary corrective steps should any one of the various temperatures or pressures exceed pre-established safe limits therefore. Obviously, such a system is highly unsatisfactory since there is room for human error in taking the readings, making the necessary comparisons and taking appropriate corrective measures in response thereto. Furthermore, such a system, which depends on human response, is dangerously slow in view of the tremendously high temperatures and pressures which can quickly build up within a device such as a multi-stage compressor.

Accordingly, in recent years there has been great emphasis on the development of multi-function systems which can quickly and accurately display the instantaneous magnitude of a plurality .of parameters associated with a particular device being monitored and which system can automatically take necessary corrective steps in the event preselected ones of such parameters exceed predetermined safe limits.

SUMMARY OF THE INVENTION The instant invention is in fact the result of a concentrated effort to improve monitoring and display systems utilized in conjunction with multi-stage compressors. To that end, the monitoring and display system of the instant invention was specifically designed to display 25 pressure and temperature check points which are crucial to the continuous operation of such a compressor. Additionally, various control functions built into the system of the instant invention are particularly tailored to shut down a compressor; relieve the air bank thereof etc., in response to predetermined alarm situations. Similarly, other functions built into the monitoring and display system of the instant invention were designed with a multistage compressor in mind and accordingly will be described in that context. However, it is to be understood that the instant invention is, in its broadest sense, directed to a system which can monitor and display the instantaneous value of a plurality of parameters associated with the operation of any desired device and additionally, is directed to such a system which has multi-functioncapabilities useful in conjunction with whatever particular device is being monitored. In a narrower sense, the instant invention relates to a monitoring and display system which has particularly advantageous characteristics when considered in conjunction with, and in the context of, the multi-stage compressor for which it was designed.

Broadly speaking, the monitoring and display system of the instant invention comprises a number of sub-systems which co-act with one another to perform a multitude of functions.

For example, there is a sensing sub-system which includes a plurality of transducers each of which produces a signal representative of the magnitude of the parameter being monitored by that transducer. There is a display sub-system responsive to the signals produced by the sensing sub-system which display system produces an accurate decimal readout of the magnitude of the various parameters monitored by the transducers. Additionally, there is a sequencing sub-system for sequentially selecting each of the transducers of the sensing sub-system whereby the display sub-system will sequentially display the magnitude of each of the parameters as corresponding transducers are sequentially energized. Thus, in accordance with a first aspect of the instant invention, a plurality of parameters are continuously and sequentially monitored with the magnitude of each of these parameters being accurately displayed in sequence at one central readout location.

As a further feature of the instant invention, the aforementioned sequencing sub-system may be operated in either a scan mode (in which each of the aforementioned transducers are sequentially selected or in a hold mode in which a particular one of the stations being monitored remains selected such that the magnitude of its respective parameter is continuously displayed. Additionally, means are provided to operate in the scan mode at either a slow" or fast" scan. Finally, the sequencing sub-system includes a plurality of energizable light indicators each of which carries appropriate indicia and corresponds to one of the stations being monitored. in this manner, when a particular station is being monitored, such that the magnitude of the parameter detected is displayed on the readout section of the system, the appropriate indicator will be energized to provide a visual indication of which station is being monitored and displayed at that particular instant.

As a further feature of the invention, there is provided a compare" sub-system in which the magnitude of preselected ones of the' monitored parameters are continuously compared to pro-established safe reference values. Should a monitored parameter exceed its predetermined level, an alarm signal is produced to energize an alarm indicator on the monitor and display panel and/or to simultaneously initiate corrective steps which take place in the control sub-system about to be described.

The control system is, as noted above, responsive to the generation of alarm signals and has as its function the responsibility for quickly and automatically taking appropriate corrective or shut down" measures when such alarm signals have been generated.

Thus, in the monitoring and display system of the instant invention which was designed in accordance with the requirements of a multi-stage compressor, the comparator subsystem generates alarm signals in three special circumstances. First, should a articular group of temperature check points exceed pre-established magnitudes or should the oil pressure of the system fall below a predetermined safe magnitude; a first alarm signal is generated and the control system, responsive thereto, will permanently shut down the motor of the system which can not be reactivated again without manual assistance. The comparator sub-system will generate a second alarm signal should the air banks pressure of the compressor exceed a predetermined maximum level. Should the second alarm signal be generated, the control sub-system will de-energize the compressors unloader control valve thereby allowing the compressor to operate in the unload condition. Furthermore, should the air banks pressure fail to fall below the preestablished maximum level within 10 minutes, the control system will then shut down the compressor motor until the air banks pressure returns to an acceptable value. Should the air banks pressure fall below a pre-established minimum level, the unloader control valve will be energized to allow the compres' sor to operate in the loaded mode to build up pressure. The

end result is that the air banks pressure will oscillate within a I given range established by the pre-established maximum and minimum values. Finally, should an especially critical first stage discharge pressure" exceed a predetermined limit during any start up operation, a third alarm signal is generated in the comparator circuit, and in response thereto, the control sub system will prevent the compressors motor from starting and prevent the unloader control valve from closing.

Thus, in another aspect of the instant invention, the comparator and control sub systems cooperate to (1) indicate the occurrence of pre-established alarm situations and to (2) take necessary corrective steps to alleviate the condition which caused the alarm.

As a further feature of the instant invention, appropriate sub systems and circuits are provided to instantaneously display the value of the particular parameter which generated an alarm condition even if another station is being displayed when the alarm occurs. Thus, regardless of whether the system is operating ina scan mode or is holding at a particular channel, when an alarm occurs, the readout system will automatically shift and display the magnitude of the parameter which caused the alarm situation and simultaneously the indicator for that particular channel will be energized to indicate which channel caused the alarm and is being displayed at that moment.

As a further feature of the instant invention, a memory sub system is provided which will continually update and retain the value of preselected ones of the parameters being monitored. Thus hours, days, or even months after a particular alarm has caused the shut down of the compressor (or any other device being monitored), an operator can return, depress the switches corresponding to the pre-established memory channels, and visually observe on the display the value of those particular parameters immediately prior to the instant of alarm. It will be appreciated that such after-gathered information frequently provides insight into the reason for the failure.

From the above, it will be seen that it is an object of the instant invention to provide a system for monitoring and displaying the instantaneous magnitude of a plurality of parameters associated with the continuous safe operation of a particular device.

Another object of the instant invention is to provide such a system which can sequencially monitor and display the value of the aforementioned parameters.

Another object of the instant invention is to provide such a system which includes means for continuously monitoring and displaying the magnitude of a selected parameter associated with a monitored device.

Yet another object of the instant invention is to provide such a system which, in addition to monitoring and displaying a plurality of parameters, also performs a plurality of other useful functions.

Another object of the instant invention is to provide such a monitoring-display system which continuously compares a plurality of monitored parameters with pre-established magnitudes and generates alarm signals should safe limits be exceeded.

Yet another object of the instant invention is to provide such a monitoring and display system which includes a control system responsive to the generation of such alarm signals corrective actions to alleviate situations which have caused alarm situations.

Another object of the instant invention is to provide such a monitoring display system which will immediately display the magnitude of a parameter which has caused an alarm situation.

Yet another object of the instant invention is to provide such a system which includes a memory sub system for retaining the value of preselected parameters for subsequent display after an alarm situation.

Another object of the instant invention is to provide such a monitoring and display system which has especially advantageous characteristics when operating in conjunction with and in a context of a multi-stage compressor.

These and other objects of the instant invention will be had by referring to the following description and drawings in which:

FIG. 1 is a front view of a display panel of a monitoring system constructed in accordance with the teachings of the instant invention;

FIG. 2 is a schematic block diagram of the monitoring and display apparatus of the instant invention;

FIG. 3 is a layout illustrating the manner in which the remaining FIGS. 4A through 13D may be positioned to correspond to the block diagram of FIG. 2; and

FIGS. 4A through 13D are schematic circuit diagrams illustrating in detail, the apparatus of the instant invention.

DISPLAY PANEL Turning to FIG. 1, there is shown the front face 10 of a monitoring and display system 12 constructed in accordance with the instant invention. As mentioned previously, the system of the instant invention was specifically designed in conjunction with a five-stage motor driven compressor and therefore, the following description will present the operation of the invention in the specific environment of such a compressor. However, it is to be understood that the instant invention is not to be limited to such environment, but insteat has application in any system where it is desired to monitor, display, and/or control a particular device.

For the purpose of understanding the invention, it is suflictient to describe a motor driven multi-stage compressor as comprising two or more compression cylinders acting in series, with the first stage taking its suction from the atmosphere or other source and discharging at a higher pressure; the second stage taking its suction from the discharge of a first stage and compressing to a still higher pressure; and so on. It is the compressed air which is exhausted from the last stage which is received and stored by the air banks of the compressor system. conventionally water cooling is used in the compressor (around the compression cylinder head and also between compression stages) to maintain the temperatures involved as low as possible.

With this background in compressors, it will be seen that the front surface 10 of the monitoring display apparatus 12 includes at its upper extremity a display readout section 14 comprising four conventional seven bar display bulbs, 16, 18, 20 and 22 respectively. As will be explained in greater detail, this display section 14 presents an accurate, visual readout of the magnitude of a particular parameter being monitored by the system 12.

Located substantially in the middle of the face 10 is a first group of push-button 26, 24 (with individual lights therebeneath) which as indicated at 25, correspond to a pluraiity of pressure locations around the compressor which are being monitored. The second push-button 30 corresponds to a station wherein the discharge pressure at the second stage of the multi-stage compressor is being monitored. Similarly, the push buttons 32 through 48 bear identifying indicia and correspond to other stations in the multi-stage compressor where it is desirable to take a measurement of pressure.

Beneath the first group of push-button 24 is a second group 50 of push-button switches (with individual lights therebeneath) each one of which corresponds to a particular location around the multi-stage compressor at which a temperature reading is to be taken. Thus, the push-button 52 corresponds to the suction or input station of the first stage of the multi-stage compressor at which a temperature reading is desirable. Similarly, the push-button 54 corresponds to the suction or input station to the second stage of the multistage compressor where a temperature reading is desirable. In kile manner, the push-buttons 56 through 78 correspond to various; stations throughout the multi-stage compressor at which it is desirable to sense temperature.

To the left of the first group of push-buttons 24 are slow and fast scan push-buttons 80 and 82 (with lights therebeneath), thefunctions of which may best be understood by considering at this time the interrelationship of the push buttons of groups 24 and 50 and the display 14.

Assuming it is desirable to sequentially monitor and display the pressures and temperatures at the various stations which have been identified by the push-button numerals 28 through 48 and 52' through 78, the operator depresses either the slow scan push-button 80 or the fast scan push-button 82 (depend ing upon the speed at which he wishes to scan the stations). If he depresses the fast scan button 82, this button will light upto indicate rapid scan and the following events occur. First the push button 28 will light up to indicate that the pressure at the first stage discharge port of the compressor was being monitored, while simultaneously the magnitude of the pressure at the first-stage discharge port would appear on the display bulbs 16-22. Four seconds later, the light in the first push button 28 will extinguish, and the light in the second push-button 30 would become energized indicating that the pressure at the second stage discharge port was now being monitored. Simultaneously, the readout on the display 14 would change to the magnitude of the pressure at second stage discharge port. This process continues with each of the 25 stations being sequentially monitored (at 4 second intervals) with the appropriate push-button being lit to indicate the channel being displayed. Furthermore, unless stopped, the cycling will continue indefinitely. If the oeprator wishes to slow down the scan, he would depress the slow scan button 80 which changes the scan interval to every 8 seconds rather then every 4 seconds.

Rather than operating in the scan mode, the operator can depress any one of the station push buttons, such that the system will switch from the scan mode to the Hold mode" with the station corresponding to the depressed push button being continuously monitored and displayed on the bulbs.

As additional zero test push button 84 is provided in the first group of buttons 24 and, as will be further described, should produce a zero reading on the dis lay bulbs whenever that zero test push button 84 is lit. Therefore, so long as a 0 continues to reappear each time the push button 84 is lit in the scan cycle, the operator knows that the system is functioning properly.

A display test" push button 86 is provided beneath the scan push buttons 80 and 82. When this button is depressed, it has the affect of causing the display 14 to display 8888 which is the maximum utilization of all seven bars in the display bulbs 16, 18, 20 and 22. Thus at any time, the operator can assure himself that the bulbs of his display 14 are functioning properly.

On the right side of the display panel 10 is provided an "off/on power push button 88; an alarm reset push button 90; and first discharge and air banks alarm push buttons 92 and 94 respectively, the functions of which will be presented in greater detail. It is sufficient at this point to note that the buttons 90, 92 and 94, and the lights located therein, provide alarmpcapability in the instant invention and indicate that preselected parameters have exceeded pre-established limits.

OVERALL SYSTEM OPERATION Turning to FIG. 2, there is shown in schematic block diagram form the monitoring and display apparatus which was broadly designated 12 in FIG. 1. The system includes a sensing system 96 which, broadly speaking, andas will be further described, includes a plurality of transducers 100 each of which produces an electrical analog signal representative of the particular parameter being sensed by that transducer. As was suggested previously, these transducers are located at the various points throughout the multi-stage compressor at which it is desirable to monitor and display parameters such as pressure and temperature.

A sequencing system 98 sequentially selects or enables the individual transducers 100 such that every 4 or 8 seconds (assuming operation in the scan mode) a different transducer will pass its analog signal to an analog to digital converter 102.

Should it be desirable to operate in the "hold" mode, depression of the desired push button on the panel 10 of FIG. 1 will direct the sequencing system 98 to seek out the appropriate transducer 100 in a sensing system 96 and continuously enable it to pass its signal to the converter 102.

At appropriate intervals, transfer logic 104 transfers the digital signals from the output of the A-to-D converter 102 to storage system 106 from which the signals pass through gating logic 108 to shifting logic 110 which directs the information to the appropriate display bulbs in the display system 14. As will be further described, the function of the shifting system 110 is to direct the digital information into the bulbs 18, 20, and 22 should a three place parameter be displayed (and blank out the first bulb 16) or alternatively to direct the infon'nation to the three most mathematically significant bulbs 16, 18 and 20 and add a 0 to the fourth bulb 22) should a four place parameter have to be displayed.

At the same time that the output of a particular transducer was being passed to the A-to-D converter 102, it might also be on its way to a comparator system 112 where preselected signals from the sensing system 96 (representative of preselected stations in the compressor) are compared with predetennined safe limits. If these safe limits are exceeded, alarm signals are generated on the output lines broadly designated 14 of the comparator 112. These alarm signals perform a number of functions such as energizing the lights in the alarm buttons 90, 92 or 94 on the panel 10 of FIG. 1 to indicate to an operator that an unsafe alarm condition exist. Additionally, such alarm signals are passed on to a control system 1 16 which broadly speaking takes steps to shut down the compressor and/or obviate the particular condition which caused the alarm.

Finally, as mentioned previously, the instant invention has memory capabilities in that it will continuously store updated values of preselected parameters which it might be useful to display at some subsequent point after an alarm situation. Thus memory logic 118 of FIG. 2 is provided to permit the information stored in auxiliary buffer devices of storage system 106 to be transferred to the display system when it is desired to display the retained information.

SENSING SUB SYSTEM As noted, the sensing system 96 includes a plurality of transducers 100 each of which produces an electrical analog signal representative of the magnitude of the parameter being sensed by the respective transducer. For the sake of clarity in the drawings, only four such transducers have been illustrated in FIGS. 4A and 4B: namely, the temperature transducers 100 100 and 100 and the pressure transducer 100 The sub scripts 52, 54, 78 and 28 are intended to indicate that the particular transducers identified in FIGS. 4A and 4B are located about the multi-stage compressor at the various stations which have been previously identified in FIG. 1 by a like numbered push button. For example, the temperature transducer 100;: would be located, according to the indicia on push button 52 of FIG. 1, at the entrance or suction port of the first stage of the multi-stage compressor to sense the temperature developed at that point. Although not completely shown in FIGS. 4A and 48, it will be appreciated that the sensing system 96 utilized in the instant invention would actually comprise l4 temperature transducers corresponding in number 100 through 100 and 1 1 pressure transducers corresponding in number to 100 through 100 Furthermore, it should be apparent that a greater number of transducers can be provided should it be desirable to monitor more than the 25 stations considered critical in the multi-stage compressor under consideration. Similarly, a less sophisticated piece of equipment might require fewer transducers to provide adequate monitoring functions. Also, parameters other than temperature and pressure can be monitored using different types of transducers available in the art.

Each of the temperature transducers 100 through 100 comprises a thermocouple preferably of the copper-constantan type, and as such includes a hot junction 120 of these two metals. By virtue of the common lines 122 and 124, all of the temperature responsive thermocouples share a common reference junction 126 which is provided with conventional temperature compensation means for correcting for changes in ambient temperature conditions. From the point of view of operation of these transducers, it is sufficient to note that each will produce an analog voltage the magnitude of which will represent the particular temperature being sensed at the hot junction 120 thereof.

Each of the pressure transducers 100 through 100., is preferably of the strain gage type and as such includes a resistive bridge 128 excited by the common l-volt lines 130 and 132. As well known in the art, the bridge 128 of such units will become unbalanced to the extent of the pressure applied to one pressure responsive resistor thereof and will generate an analog voltage signal on the lines 134 and 136 which is representative of the pressure sensed. The output lines 134 and 136 from each pressure transducer are connected through normally open contacts such as 158 to common lines 138 and 140.

In their preferred embodiment, each of the pressure transducers 100 through 100 includes an individual gain adjustment means 142 in the form of a multi-tum minature potentiometer provided with a selectively positionable tap whereby the gain of the individual pressure transducers can be individually adjusted. Similarly, each pressure transducer includes a zero adjustment means 144 similarly in the form of a minature multi-turn potentiometer provided with a positionable tap. The zero adjustment means 144 is customarily used in the initial set up procedure by applying zero pressure to the transducers 134 and 136 to generate a zero signal on lines 134 and 136 which by definition represents a zero pressure (atmospheric pressure). When this zero pressure is applied, the tap of the multi-tum potentiometer 144 is then varied until the display system 14 visually presents 0 on its bulbs.

Finally, each of thepressure transducers includes a filter network 146 the components of which are selected to filter variations approximately 15 cycles per second and above which also happens to be the normal frequency variation in the pressure responsive system. Thus, the selection of IS cycles per second eliminates all noise in that frequency range while at the same time eliminates undesirable frequency variations in the transducer output.

TRANSFER FROM THE SENSING SYSTEM TO THE AN ALOG-TO-DIGIT AL CONVERTOR As will be described in greater detail, the sequencying system 98 of FIGS. ISA-13D includes a plurality of output channels 148 which for the sake of uniformity of numbering, are designated 148 through 148 to suggest the fact that each of the output channels corresponds to one of the transducers in the sensing system 96. Taking output channel 148 for example, it is sufficient to point out at this time that as each channel is energized, there will be a low signal, such as illustrated at the take off point 148 and by virtue of an inverter 150, there will be high signal (148 utilized to turn on a transistor 152 which permits the energization of a coil 154 and simultaneously the energization of an indicating light bulb 156 which are in fact the indicating lights positioned beneath the push buttons 28 through 78 of FIG. 1.

The coil 154 of each channel 148 controls a respective pair of normally open contacts such as 158,; in the sensing system 96 of FIG. 43. It is to be understood that each coil 154 of the respective output channels 148 controls a similar pair of normally open contacts in the particular transducer circuit which corresponds to that particular channel.

Also to be described further is the fact that the sequencing system 98 includes means for sequentially selecting each of the channels 148 through 148 Therefore, as each channel is energized the following events take place. Considering channel 148 of FIG. 13D as illustrative, high signal 148 turns on transistor 152 and permits the energization of the coil 154 and the indicating light 156. When coil 154 is energized, the contacts 158 in sensing system 96 controlled thereby, close to enable the pressure transducer 100 to pass the pressure representing voltage signal along the common lines 138, to a pressure amplifier'160 (FIG. 4A). Thus the signal representative of the pressure at the discharge port of the first stage of the multi-stage compressor is on its way to be displayed by the display system. Simultaneously, the energization of the light 156 positioned beneath the push button 28 on the panel 10 reading on the display 14 corresponds to the pressure at the first stage discharge port.

Thus, with the system operating in the scan mode, every 4 or 8 seconds one of the channels will be sensed and displayed.

In the event a temperature channel such as 148 happens to be energized, its respective coil 154 will be energized to close contacts 158,; in sensing system 96, to pass the analog signal representative of temperature along common lines 122 and 124 through the common reference junction 126 and on toa temperature amplifier 162.

The amplifiers and 162 are preferably conventional DC operational amplifiers of the integrated circuit type and as suggested in FIG. 4A are gain controlled by feedback resistors which are externally connected. The amplifiers raise the millivolt output of the respective transducers to approximately a 5 volt level which signals are then passed by the following described circuitry, to the analog-to-digital convertor 102.

Specifically, whenever a pressure channel (such as 148 148 of the sequencing system 98 is energized; the low signal produced therein (for example 148 of FIG. 13D) is applied to a line such as 164 in the sensing sub system 96 of FIG. 4A which, through the inverter 166, applies a high to a transistor 168 to energize a coil 170 the nonnally open contacts 172 of which will close to pass the output of the pressure amplifier 160 along the line 174 to the analog-to-digital converter 102 of FIG. 5. Should a temperature channel such as 148 be energized, it will be appreciated that no signal will be applied to the inverter 166 of FIG. 4A and therefore a low signal will appear at its output. However, this low signal is inverted by inverter 176 to turn on transistor 178 which in turn brings about the energization of the coil 180 whose normally open contact pair 182 will close to pass the signal developed at the output of the temperature amplifier 162 on to the line 174 and to the analog-to-digital converter 102. It may be pointed out that at the output of temperature amplifier 162 there is provided a shaping network 184 to linearize the signal representing temperature.

ANALOG DIGITAL CONVERSION Although not specifically illustrated in the block diagram of FIG. 2, the system of the instant invention employs a pulse generator 186 (see FIG. 12) which produces at output terminals 188, 190, and 192 pulses which are designated E" pulses, D pulses, and F ulses respectively. The purpose of each of these pulses will become further apparent as the description of the system unfolds.

Considering the analog-to-digital converter and with reference to FIG. 5, 30 times per second an E pulse is applied to the terminal 194 of the A to-D converter to initiate a conversion process. The A-to-D converter is a conventional device responsive to analog signals and produces as an output three groups of digital signals 196, 198 and 200 each of which, in four line binary form, represents one decimal digit of a three digit number.

Each time the conversion process is complete, an end of conversion pulse 202 is produced on an output line 204 (see also FIG. 6). The manner in which the numbers represented by the three, four line groups 196, 198, and 200 are transferred to the storage system 106 is controlled by the transfer logic 104 in the following manner.

9 TRANSFER LOGIC The transfer logic 104 of FIG. 6 includes a flip-flop 206 and gates 208 210, 212, 214, and 216 which operates as follows: With the generation of a coincidence pulse 220 (to be described) flip flop 206 is enabled (to apply one signal via line 207' to pin 222 of gate 216) such that an end of conversion pulse 202 developed on the line 204;passes through gate 208 and is applied by line 224 as the second enabling signal to gate 216. Thus, the output line 228 of the gate 216 will go low and enable main bufier storage devices 230, 230 and 230" of the storage system 106 of FIG. 7 to receive the respective groups of signals 196, 198 and 200. In this manner, each of the main buffer storage devices will receive and retain a four bit binary signal representing one mathematical place of a three place number which, as previously described, corresponds to the particular parameter which happens to be monitored at the particular instant of time when the end of conversion pulse 202 was applied to gate 216. In addition the end of conversion pulse 202 resets flip flop 206 which then awaits the next coincidence pulse 218.

It will be appreciated that for the sake of drawing clarity, only the four lines 232, 234, 126 and 238 of the signal group 196 of FIGS. and 6 have been fully shown as directly passing to the main buffer storage device 230. Similar connections are suggested in FIG. 6 and do, in fact, exist between the signal groups 198 and 200 of FIG. 5 and the respective main buffer storage devices 230 and 230 of FIG. 7.

MEMORY FUNCTION As noted previously, it is a feature of the instant invention that the last value of preselected ones of the parameters being monitored can be stored and subsequently displayed after an alarm situation. To that end the storage system 106 of FIG. 7 includes auxiliary buffer storage devices 240, 240', 240"; 242, 242 and 242"; and 244, 244 and 244. Before going into detail, it might be pointed out that in the instant system, by design, the auxiliary buffer storage devices 240, 240 and 240" will store the third stage discharge temperature of the compressor; auxiliary buffer storage devices 242, 242 and 242" will store the fourth stage discharge temperature; and auxiliary buffer storage devices 244, 244' and 244 will store the fifth stage discharge temperature.

Returning to the sequencing system 98 of FIG. 13D, let it be assumed that the system is operating in the scan mode in which each of the output channels 148 will be sequentially energized to perform the functions previously described. When the scanning gets up to output channel 148 for example, in addition to the respective coil 154 and indicator 156 becoming energized, an additional line such as 246 will go high to apply a signal to pin 248 of the gate 210 of transfer logic 104 of FIG. 6. Therefore, upon the generation of the next end of conversion pulse 202 (signifying that the analog voltage representative of the 3rd stage discharge temperature developed at transducer 100 has passed through respective contacts such as 158 and has been converted to digital form) line 224 will go high, so as to apply an enabling pulse not only to the gate 216 of FIG. 6 but also to the gate 210. Therefore, with the gate 216 enabled (by the application of pulses on pins 222 and 226) and gate 210 enabled (by the application of signals on lines 246 and 224); the net result is that enabling signals appear not only on the output line 228 to enable the main bufier storage devices, but also on a line 250 to enable the third stage discharge auxiliary bufier storage devices 240, 240' and 240".

Thus each time the output channel 148 of the sequencing system 78 is energized, the magnitude of the 3rd stage discharge temperature will pass to the main buffer devices 230, 230' and 230" and simultaneously to the auxiliary buffer storage devices 240, 240' and 240". To be described sub sequently in the manner in which this additionally stored information can be displayed after an alarm situation has occurred.

A similar operation takes place when channel 148 of FIG. 13D energized during a scan cycle with the magnitude of the fourth stage discharge temperature being transmitted from the respective transducer through the respective contacts 158 through the temperature amplifier 162 and to the analog-todigital converter 102). Thus, in addition to energizing the coil 154 and indicator light 156 of the output channel 148 an additional line 252 goes high to apply a signal to the gate 212 of FIG. 6. Thus, on the next end of conversion pulse 202, line 224 goes high to enable gate 212 which drives line 254 high to enable the auxiliary storage buffer devices 242, 242', and 242" to receive and store the signals representative of the fourth stage discharge temperature. At the same time, the main bufler storage devices 230, 230', and 230" are enabled by the high signal on the line 228 as previously described. Again the net result is to transfer the three groups of binary signals representing the fourth stage discharge temperature to the auxiliary buffer storage devices as well as to the main buffer storage devices.

Finally, whenever the output channel 148,, of the scanning system 98 is energized, so as to sense the 5th stage discharge temperature; similar circuitry enables the gate 214 (as well as 216) such that the magnitude of the fifth stage discharge temperature will be passed not only to the main bufi'ers 230, 230' and 230 but also to the fifth stage auxiliary storage buffer devices 244, 244' and 244".

Summarizing, as the various output channels 148 through 148 of FIG. 13D are sequentially energized, the magnitude of the parameters sensed by the corresponding transducers are sequentially placed in the main storage buffer devices 230, 230' and 230, each device receiving four bits of binary information representative of one decimal number. If the particular channel energized happens to be one such as 148 148 or 148 wherein it has been predecided to store the value of such corresponding parameter, the parameter will be additionally stored in one of the respective auxiliary bufier storage devices such as 240, 242, 244 and their respective primed devices.

TRANSFER FROM STORAGE TO DISPLAY Assuming there is no alarm situation generated in the comparator system 112 of FIG. 11, gating circuitry broadly designated 108 (FIG. 8) is utilized to transfer the information from the main buffer storage devices 230, 230' and 230" to the shifting circuitry 110 (FIG. 9) which in turn applies such information to the display section 14 of FIG. 10.

The gating circuitry 108 includes 3 banks of gates 256, 258, and 260, one for each of the three decimal numbers. Each bank (for example, 260) includes four smaller banks of gates such as 262, 264, 266 and 268. Each smaller bank such as 262 includes four individual gates such as 270, 272, 274 and 276. It should be noted that in the interest of simplifying the Figures, only one such sub-bank 262 has been illustrated in detail, it being understood however, that the following description would be applicable to each of the sub-banks 264, 266, and 268 within a larger group of banks 256, 258 and 260.

For the sake of explanation, let it be assumed that the main buffer storage devices 230, 230 and 230" presently store the magnitude 367 which is representative of the particular parameter being sensed. Thus, and considering the main buffer storage device 230 which would be storing the decimal number 3, output lines 278, 280, 282, and 284 thereof would be presented with the bits of information 001 1. Thus, the voltage representing 0 on line 278 is passed to one input of the gate 270, the other input of which is maintained high by a signal appearing, in a manner to be further described, on output line 286 of memory logic circuitry 118. With gate 270 enabled, the 0 signal appears on line 288.

Similarly, the voltage-representing the 0" on line 280 of buffer device 230, passes through corresponding gate 270 of bank 264 such that a 0" voltage appears on the output line 290. In like manner, the l s appearing on lines 282 and 284 are transferred through the corresponding gates 270 (not 1 1 12 shown) of banks 266 and 268 such that the respective 1" energive the seven bar display bulb 20in accordance with the signals appear on the lines 292 and 294 of bank 256. In this magnitude of the decimal number represented by the group of manner the four bit binary representation of the decimal numsignals on the lines 298. beral 3" has been transferred from the main storage bufier Since it has been assumed that the display system 14 is device 230 through the gating logic 108. 5 presenting a four place mathematical figure, means must be Similar events take place with respect to the main bufier provided to cause the fourth display bulb 22 of FIG. to disstorage devices 230 and 23" such that the second and third play a 0. This is accomplished by applying on overriding 0 decimal numbers will appear on the four line groups 296 and signal at the input terminal 367 of the fourth four bit-to-seven 298 at the output of the banks 258 and 260. converter 368 which signal is derived from a line 369 which is 10 high whenever the line 314 of flip-flop 310 of FIG. 9 is high, SHXFHNG LOGIC indicating, as noted previously, that a four place number is to be displayed. This 0 regardless of the fact that the group of signals broadly designated 298 are simultaneously being applied to the gates 370, 372, 374, and 376 of FIG. 9. In effect, the 0 signal on the line 369 over powers the signals which As may be appreciated from the description thus far, the instant invention produces at the output of the gating circuitry 108, a three digit number (represented in binary form). How- 115 ever, some of the parameters being monitored require-four mathematical places to represent them (i.e., their magnitude is greater than 999), while others of the parameters require 1 e less 999 mawmde) Thus means must be 300 through 306 of the shifting logic 110 of FIG. 9 such that the flip flops 310 and 312 will be switched and the respective pairs of lines 314, 316; 318, 320 will reverse their high and low condition respectively. Thus, dealing with the group of signals 2 5 broadly designated 296, it will be seen that when line 314 goes low, gates 340, 342, 344, and 346 will be disabled, while (because line 320 has gone high) gates 348, 350, 352 will be enabled. Therefore, the signal represented by group of lines 296 will be shifted one place and be passed through the last mentioned gates to the four bit-seven bit converter 366 of FIG. 10 whereby appropriate signals will then be applied to bulb: namely bulbs 16, 18, and 20 (and force a on bulb 22) if a four placed parameter is to be displayed; or bulbs 18, 20 and 22 (and blank the display bulb 16) if a three placed parameter is to be displayed.

In the instant system, it is known that the fourth stage discharge pressure, the fifth stage discharge pressure, the air banks pressure, and the accumulated pressure may all have a magnitude of 1,000 or greater psi. Therefore, whenever one of these stations is being monitored, the shifting logic 110 of FIG. 9 must provide that the three decimal numbers (represented the Seven bar display bulb 20 in binary form) appearing at the output of the gating circuitry Similarly when line 318 of flip flop 312 goes low gates 358 108 be shifted directly to the bulbs 16, 18 and 20 and means 360 362 a 364 will be must be provided for causing the least mathematical significant bulb 22 to display a 0". Should any other station be the gates 370 372, 374

monitored, the shifting circuitry must be such as to direct the converter 368 of FIG 10 and the to the Seven bar display Place quantity the bulbs and 22 and bulb 22. (Ofcourse the high line 369 ofFIG. 10 now goes low propriate means must be provided to blank out the most because line 314 offllpflop 310 has gone low),

mathemaucauy slgnfficam dlsplay bulb 40 With respect to the 0011 signal appearing on lines 288 As discussed previously, whenever one of these four stations through 294, these Signals will be applied thmuglnhe gates are being monitored, the corresponding output channel of the 322, 328, 330 and 322 to the four blt to seven bit Convener sequencing system 98 of FIG. 13D (i.e., output channels 340 of FIG 10 and illsO to the converter 356 through the 148 148 148 148 will be energized so as to apply the gates 326, 334, 336 and 338 which are enabled by the high corresponding 10w slgna] (14834L l48361- the now appearing on line 316. However, a blanking signal carried line 300, 302, 304, or 306 respectively of the shifting logic 110 by the line 378 of FlG. 10 will be applied to the converter 3 of FIG. 9. In response to the application of such a low signal, 110 override signals being applied by gates 2 328, 330 gating circuitry designated 308 influences a pair of flip flops d 332, I may be appreciated that he high pp ring on lin 310 and 312 to produce high and low signals respectively on 378 f a 10 and being applied to the converter 34 a an th lines 320 to perform the following input terminal 380 thereof, is derived from the high which Q now appears on the line 320 of the flip flop 312 by virtue of Assllllllllglhal a foul Place Parameler ls to be dlsplayedt a the fact that a three place number, and not a four place high appears on the line 314 to enable gates 340, 342, 344, number, is being Sense 346; and a high on line 318 enables gates 358, 360, 362 and ll will be appreciated that by virtue f h "bl lw d Similarly, a low will pp on the line 316 to disable zero" signals utilized on the lines 378 and 369 respectively, it Sales 326, 334, 336, 333 and a low line 320 dlsables Sales is: possible to eliminate the duplicate set of gates which were i and Gales 324, i 330 and 332 are required for the middle two mathematical places. Furthery enabled and, accordingly the slgllal 0011 representing more, such arrangement compensates for the fact that certain the decimal number 3 will be shifted directly through the gates of the transducers (monitoring pressures over 1,000 psi) have 330 and 332 to a foul bll-lo-sevell line Converter adifferent output sensitivity. Thus the output of these transduconverts the fOul' information into cars difi'ers from those monitoring less than psi a fag. corresponding seven line information which in turn is applied tor of 10 for which the shifting logic inherently compensates. to the seven bar display bulb 16 which will thereby display the Finally, with respect to the display, it was noted previously decimal number 3 on the bulb 16. 5 that there is a display test push button provided on the panel h the gates 344 and 346 enabled y the g 10 of FIG. 1. This push button 86 shows diagramatically in on line 314, the signals appearing on the group of lines broadly FIG. 10 and when depressed, influences gating broadly designated 296 will pass directly to a second four bit-to-seven designated 382 to develop high signals on the lines 384, 386, converter 356 of FIG. 10 which in turn will apply appropriate 388 and 390. These high signals are applied to the respective signals to the second display bulb 18 which will display the input terminals 392, 394, 396 and 398 respectively to cause decimal number represented by the group of 296- the converters to apply high signals to each of the seven inputs Finally, the high signal on line 318 will enable gates 358, of each of the bulbs 16, 18, 20, and 22. The net result is that 360, 362 and 364 such that the signals on the group of lines the display will read 8888 whenever the display push button broadly designated 298 will pass directly to a four bit-to-seven 86 is depressed. Should any bar lights be out when that button bit converter 366 which will produce the necessary signals to is depressed, it will become immediately apparent. 

1. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; each of said signals produced by said plurality of transducers is an analog voltage signal the magnitude of which represents the instantaneous value of the respective parameter which said transducer is monitoring; wherein said display means includes analog to digital conversion means for converting said analog voltage signal to a corresponding digital signal as said analog signals are sequentially presented to said display means; wherein said display means first includes display bulb means responsive to said digital signal for visibly displaying the decimal value of said digital signal; and further including: pulse generator means for producing a repetitive initiation pulse which is applied to said analog-to-digital conversion means to initiate the conversion process; said A-D conversion means producing an end of conversion pulse each time said conversion process is complete; main buffer storage means intermediate said A-D conversion means and said display bulb means for temporarily storing said digital signal and impressing same on said display bulb means; read pulse generating means for generating a repetitive read pulse at a predetermined interval of time; and enabling logic circuit means responsive to the simultaneous occurrence of one of said read pulses and one of said end of conversion pulses for enabling said main buffer storage means to receive and store said digital signal from said A-D conversion means.
 2. The apparatus of claim 1 and further including auxiliary buffer storage means intermediate said A-D conversion means and said display bulb means for storing predetermined ones of said digital signals until some predetermined subsequent time when it may be desirable to display the value stored in said auxiliary buffer storage means; said enabling logic means being further responsive to said sequencing means and the occurrance of one of said end of conversion pulses for enabling said auxiliary buffer storage means to receive said predetermined ones of said digital signals corresponding to particular parameters the latest magnitudes of which it is desired to retain for subsequent display.
 2. to close the aumiliary contact pair thereof to pass the corresponding preselected reference voltage to said first comparator means.
 3. The apparatus of claim 1 wherein during each conversion process said A-D conversion means produces a predetermined number of groups of digital signals representative of a decimal number have said predetermined number of mathematical places; and wherein said main buffer storage means includes a plurality of main storage devices equal in number to said predetermined number of groups and wherein said display bulb means includes a plurality of display bulbs equal in number to at least one more than said predetermined number of groups; and wherein said enAbling logic circuit means enables each of said plurality of main storage devices to receive one of said plurality of groups.
 4. The apparatus of claim 3 and further including auxiliary buffer storage means intermediate said A-D conversion means and said display bulb means, said auxiliary buffer storage means comprising a first plurality of auxiliary storage devices equal in number to said predetermined number of groups; said enabling logic means further responsive to said sequencing means and the occurrance of one of said end of conversion pulses for additionally enabling said first plurality of auxiliary storage devices to respectively receive and store said predetermined number of groups of digital signals when it is desired to retain and store the latest magnitude of a preselected parameter for subsequent display.
 5. The apparatus of claim 4 wherein said auxiliary buffer storage means includes a second plurality of auxiliary storage devices equal in number to said predetermined number of groups; said enabling logic means being further responsive to said sequencing means and the occurrance of one of said end of conversion pulses for additionally enabling said second plurality of auxiliary storage devices to respectively receive and store said predetermined number of groups of digital signals when it is desired to retain and store the latest magnitude of a different preselected parameter for subsequent display.
 6. The apparatus of claim 4 wherein at least one of said parameters customarily requires at least one more than said predetermined number of mathematic places to represent its magnitude, and further including display logic circuit means responsive to the monitoring of said one of said parameters for transferring said groups of digital signals representative of said one of said parameters from said plurality of main storage devices to respective ones of a first group of said display bulbs equal in number to said predetermined number of mathematical places and for causing an additional display bulb, less significant in terms of its mathematical place with respect to said first group of said display bulbs, to display a ''''0''''.
 7. The apparatus of claim 6 wherein said display logic circuit means will transfer groups of said digital signals from said plurality of auxiliary storage devices to respective ones of said first group of said display bulbs and will cause said additional bulb to display a ''''0'''' when it is desired to display one of said preselected parameters which have been stored in said auxiliary storage devices and said preselected parameter requires at least one more than said predetermined number of mathematic places to represent its magnitude.
 8. The apparatus of claim 6 wherein the group of digital signals stored in the mathematically ''''least significant'''' main storage device will be transferred to the two mathematically least significant display bulbs; and wherein said display logic circuit means provides an overpowering ''''0'''' signal to the least significant of said two display bulbs when one of said parameters which requires one more than said predetermined number of places is being monitored.
 9. The apparatus of claim 6 wherein others of said parameters require only said predetermined number of mathematic places to represent their magnitude; and wherein said display logic circuit means transfer said groups of digital signals from said main storage devices to respective ones of a second group of said display bulbs equal in number to said predetermined number of places and causes a mathematically more significant one of said display tubes to display a blank.
 10. The apparatus of claim 9 wherein said group of digital signals stored in the mathematically ''''most significant'''' main storage device will be transferred to the two mathematically most significant display bulbs and wherein said display logic circuit means will produce a overpowering ''''blanking'''' signal whiCh will cause the most significant of said two bulbs to display a ''''blank''''.
 11. The apparatus of claim 9 wherein said display logic circuit means will transfer groups of said digital signals from said plurality of auxiliary storage devices to respective ones of said second group of said display bulbs and will cause said mathematically more significant one of said display tubes to display a blank.
 12. The apparatus of claim 3 wherein at least one of said parameters customarily requires at least one more than said predetermined number of mathematic places to represent its magnitude, and further including display logic circuit means responsive to the monitoring of said one of said parameters for transferring said groups of digital signals representative of said one of said parameters from said plurality of main storage devices to respective ones of a first group of said display bulbs equal in number to said predetermined number of mathematical places and for causing an additional display bulb, less significant in terms of its mathematical place with respect to said first group of said display bulbs, to display a ''''0''''.
 13. The apparatus of claim 12 wherein others of said parameters require only said predetermined number of mathematic places to represent their magnitude; and wherein said display logic circuit means transfers said groups of digital signals from said main storage devices to respective ones of a second group of said display tubes equal in number to said predetermined number of places and causes a mathematically more significant one of said display tubes to display a blank.
 14. The apparatus of claim 2 wherein said sequencing means includes: a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; and wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; and wherein said enabling logic means for enabling said auxiliary buffer storage means is responsive to the occurrance of one of said end of conversion pulses and to the energization of the output channel of said sequencing means which corresponds to the transducer which is monitoring the particular parameter the latest magnitude of which it is desired to retain for subsequent display.
 15. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; said output channels including primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of each of said channels being normally de-energized and being energized only when its respective output channel is energized by said sequential energizing means; a first plurality of said transducers are monitoring a first parameter and a second plurality of said transducers are nomitoring a second parameter; and further including additional enabling logic circuit means responsive to the energization of any one of said output channels which corresponds to a transducer in said first plurality of transducers for permitting signals generated by any one of said first plurality of transducer to pass to said display means; and said additional enaBling logic circuit means being further responsive to the energization of any one of said output channels which corresponds to a transducer in said second plurality of transducers for permitting signals generated by any one of said second plurality of transducers to pass to said display means.
 16. The apparatus of claim 15 wherein said additional enabling logic circuit means includes: a first normally de-energized coil having a normally open contact pair interposed between said first plurality of transducers and said display means; a second normally de-energized coil having a normally open contact pair interposed between said second plurality of transducers and said display means; and inverter means disposed before said second coil; energization of any one of said output channels which corresponds to a transducer in said first plurality of transducers causing the energization of said first coil which closes its respective contact pair to complete a circuit from said first plurality of transducers to said display means; non-energization of any one of said output channels which corresponds to a transducer in said first plurality of transducers causing said inverter means to energize said second coil which thereby closes its respective contact pair to complete a circuit from said second plurality of transducers to said display means.
 17. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; said plurality of transducers are monitoring various variable parameters associated with the operation of a motor driven device; further including motor disabling circuit means responsive to the occurrence of said first alarm signal for shutting down said motor; further including second comparator means responsive to the signals produced by preselected ones of a second group of said transducers and other preselected reference signals for providing additional alarm signals when any one of said signals produced by said preselected ones of said second groups of transducers exceeds its corresponding other reference signals; wherein said second group of transducers monitor various pressure locations of a motor driven multi-stage compressor; and wherein said second comparator means includes an air bank comparator responsive to the signal produced by one of said second group of transducers which monitors air banks pressure and to adjustable minimum and maximum air banks pressure reference voltage signals for producing an air banks control signal when the signal produced by said air banks monitoring transducer falls below or exceeds said minimum and maximum air banks pressure voltage signals.
 18. The apparatus of claim 17 wherein said motor driven device is a multi-stage compressor.
 19. The apparatus of claim 17 wherein said motor is in electrical series with a pair of motor control contacts which are normally maintained closed by the energization of a motor control coil; said disabling circuit means causing the de-energization of said motor control coil upon the reception of said first signal.
 20. The apparatus of claim 19 wherein said motor control coil is in electrical series with at least one semi-conductor controlled rectifier, the control gate of which normally maintains said SCR conducting, said control gate being in electrical series with a pair of control gate contacts normally maintained closed by the energization of a control gate contact coil; said disabling circuit means causing the de-energization of said control gate contact coil upon the reception of said first alarm signal.
 21. The apparatus of claim 20 and further including a source of AC power for said apparatus, and wherein said motor control coil is in electrical series with a second SCR which conducts current to said motor control coil during the second half of an AC cycle; the control gate of said second SCR normally maintaining said second SCR conducting by being in electrical series with a second pair of control gate contacts normally maintained closed by the energization of said control gate contact coil.
 22. The apparatus of claim 21 and further including rectifying means responsive to said AC power source for producing a plurality of preselected DC voltage levels utilized in said apparatus.
 23. The apparatus of claim 21 and further including pulse generator means for producing a repetitive ''''zero voltage'''' pulse at each instant in time that said SCR''s experience zero voltage thereacross; and said disabling circuit means includes gate means responsive to the simultaneous application of said first alarm signal and one of said ''''zero voltage'''' pulse for de-energizing said control gate contact coil; whereby the conduction state of said SCR''s will be changed only when they are experiencing zero voltage thereacross to thereby reduce transients.
 24. The apparatus of claim 18 wherein said first group of transducers monitor a preselected group of temperatures associated with preselected locations of said multi-stage compressor.
 25. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; and wherein each of said output channels includes primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of each of said channels being normally de-energized and being energized only when its respective output channel is energized by said sequential energizing means; wherein sais preselected reference voltages are established by a plurality of adjustable potential sources; further including circuit means for conveying the signals produced by said preselected ones of said first group of transducers to said first comparator means; and further including reference voltage enabling means responsive to the energization of the output channels corresponding to said preselected ones of said first group of transducers for applying the corresponding reference voltage to said first comparator means; wherein each of said enabling means comprise a normally de-energized primary coil having a normally open primary contact pair in the circuit of its corrEsponding transducers; energization of said coil, in response to energization of its respective output channel by said sequential energizing means, closing said normally open contact pair to allow said signal to pass from said transducer, and wherein said reference voltage enabling means comprises a plurality of auxiliary coils each being in electrical parallel with the normally de-energized primary coil of the primary enabling means of the output channels which correspond to said preselected ones of said first group of transducers, and each of said auxiliary coils having an associated normally open auxiliary contact pair interposed between a respective one of said adjustable potential sources and said first comparator means; energization of one of said output channels which corresponds to one of said first group of preselected transducers energizing said channel''s primary coil and its aumiliary coil to
 26. The apparatus of claim 25 wherein each of said auxiliary coils includes a second associated normally open contact pair which normally prevents a gating pulse from being applied to a normally inhibiting device which also receives said first alarm signal as an input thereto; energization of one of said auxiliary coils additionally causing the closing of its respective second contact pair to permit a gating pulse to be applied to said inhibiting device such that if a first alarm signal is produced by said first comparator means, said first alarm signal will be passed through said inhibiting device.
 27. The apparatus of claim 26 and further including reset means for returning said normally inhibiting device to its blocking condition.
 28. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; second comparator means responsive to the signals produced by preselected ones of a second group of said transducers and other preselected reference signals for providing additional alarm signals when any one of said signals produced by said preselected ones of said second groups of transducers exceeds its corresponding other reference signals; wherein said second group of transducers monitor various pressure locations of a motor driven multi-stage compressor; wherein said second comparator means includes an oil pressure comparator responsive to the signal produced by one of said second group of transducers which monitors oil pressure and to an adjustable oil pressure reference voltage signal for producing a low oil pressure alarm signal when the signal produced by said oil pressure monitoring transducer falls below said oil pressure reference voltage signal; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; whErein each of said output channels includes primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of each of said channels being normally de-energized and being energized only when its respective output channel is energized by said sequential energizing means; further including circuit means for conveying the oil pressure signal produced by said oil pressure monitoring transducer to said oil pressure comparator; and further including a normally inhibiting device which prevents said low oil pressure alarm signal from passing further into said apparatus unless the output channel corresponding to said oil pressure monitoring transducer has been energized.
 29. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; second comparator means responsive to the signals produced by preselected ones of a second group of said transducers and other preselected reference signals for providing additional alarm signals when any one of said signals produced by said preselected ones of said second groups of transducers exceeds its corresponding other reference signals; said second group of transducers monitor various pressure locations of a motor driven multi-stage compressor; said second comparator means includes an oil pressure comparator responsive to the signal produced by one of said second group of transducers which monitors oil pressure and to an adjustable oil pressure reference voltage signal for producing a low oil pressure alarm signal when the signal produced by said oil pressure monitoring transducer falls below said oil pressure reference voltage signal; motor disabling circuit means responsive to the occurrence of said low oil pressure alarm signal for shutting down said motor; and first adjustable delay means for preventing said low oil pressure alarm signal from being passed to said motor disabling circuit means until some predetermined time has elapsed after said motor is restarted.
 30. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; second comparator means responsive to the signals produced by preselected ones of a second group of said transducers and other preselected reference signals for providing additional alarm signals when any one of said signals produced by said preselected ones of said second groups of transducers exceeds its corresponding other reference signals; said second gRoup of transducers monitor various pressure locations of a motor driven multi-stage compressor; and comparator means includes an air banks comparator responsive to the signal produced by one of said second groups of transducers which monitors air banks pressure and to adjustable minimum and maximum air banks pressure reference voltage signals for producing an air banks control signal when the signal produced by said air banks monitoring transducer falls below or exceeds said minimum and maximum air banks pressure voltage signals.
 31. The apparatus of claim 30 wherein said adjustable minimum and maximum air banks pressure reference voltage signals are established by: a first potentiometer which establishes the maximum voltage signal; a second potentiometer which, together with said first potentiometer, establishes said minimum air banks pressure voltage signal; and circuit means for connecting said first and second potentiometers in electrical parallel whenever the signal produced by said air banks pressure monitoring transducer exceeds said maximum voltage signal, and for disconnecting said second potentiometer from said first potentiometer when the signal produced by said air banks pressure monitoring transducer falls below said minimum voltage signal.
 32. The apparatus of claim 30 and further including compressor disabling means responsive to said air banks alarm signal for unloading said compressor.
 33. The apparatus of claim 32 and further including motor and compressor disabling means responsive to the existance of said air banks alarm signal for a predetermined interval of time for shutting down said motor and unloading said compressor.
 34. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; second comparator means responsive to the signals produced by preselected ones of a second group of said transducers and other preselected reference signals for providing additional alarm signals when any one of said signals produced by said preselected ones of said second groups of transducers exceeds its corresponding other reference signals; said second group of transducers monitor various pressure locations of a motor driven multi-stage compressor; said second comparator means includes an oil pressure comparator responsive to the signal produced by one of said second group of transducers which monitors oil pressure and to an adjustable oil pressure reference voltage signal for producing a low oil pressure alarm signal when the signal produced by said oil pressure monitoring transducer falls below said oil pressure reference voltage signal; and said second comparator means includes an air bank comparator responsive to the signal produced by one of said second groups of transducers which monitors air banks pressure and to adjustable minimum and maximum air banks pressure reference voltage signals for producing an air banks control signal when the signal produced by said air banks monitoring transducer falls below or exceeds said minimum and maximum air banks pressure voltage signals.
 35. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producinG a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; second comparator means responsive to the signals produced by preselected ones of a second group of said transducers and other preselected reference signals for providing additional alarm signals when any one of said signals produced by said preselected ones of said second groups of transducers exceeds its corresponding other reference signals; said second group of transducers monitor various pressure locations of a motor driven multi-stage compressor; and said second comparator means includes a first stage discharge comparator responsive to the signal produced by one of said second groups of transducers which monitors first stage discharge pressure and to an adjustable first stage pressure reference voltage for producing a first stage alarm signal when the signal produced by said first stage discharge pressure monitoring transducer exceeds said adjustable first stage pressure reference voltage.
 36. The apparatus of claim 34 wherein said second comparator means includes a first stage discharge comparator responsive to the signal produced by one of said second group of transducers which monitors first stage discharge pressure and to an adjustable first stage pressure reference voltage for producing a first stage alarm signal when the signal produced by said first stage discharge pressure monitoring transducer exceeds said adjustable first stage pressure reference voltage.
 37. The apparatus of claim 35 and further including motor and compressor disabling means responsive to the existance of said first stage discharge alarm signal for preventing operation of said motor during a start up operation.
 38. The apparatus of claim 37 wherein said second comparator means includes an oil pressure comparator responsive to the signal produced by one of said second group of transducers which monitors oil pressure and to an adjustable oil pressure reference voltage signal for producing a low oil pressure alarm signal when the signal produced by said oil pressure monitoring transducer falls below said oil pressure reference voltage signal; and further including motor disabling circuit means responsive to the occurrence of said low oil pressure alarm signal for shutting down said motor; and further including first adjustable delay means for preventing said low oil pressure alarm signal from being passed to said motor disabling circuit means until some predetermined time has elasped after said motor is restarted; and further including circuitry for activating said first adjustable delay means once said motor is restarted after having been shut down by said motor and compressor disabling means.
 39. The apparatus of claim 35 and further including energizable indicating means responsive to said first stage alarm signal for providing a visable indication thereof.
 40. The apparatus of claim 38 and further including circuit means for activating said first adjustable delay means in the event said motor is shut down by some means other than the activation of said motor disabling means or said motor and compressor disabling means and then restarted.
 41. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; wherein each of said output channels including primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of each of said channels being normally de-energized and being energized only when its respective output channel is energized by said sequential energizing means; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; and further including circuit means responsive to the occurrence of said first alarm signal for stopping said sequential energizing means at the output channel which corresponds to the transducer whose output signal caused said first alarm signal.
 42. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; each of said output channels including primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of each of said channels being normally de-energized and being energized only when its respective output channel is energized by said sequential energizing means; first means for sequentially maintaining each of said output channels energized for a preselected length of time; second means for sequentially energizing each of said output channels within a period of time less than said preselected length of time each time said first means maintains one of said channels; and selectable scan control timer means for varying the magnitude of said preselected length of time.
 43. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signals of the magnitude of one of said variable parameters; display means responsive to any one of said signal s for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; said output channels including primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of eAch of said channels being normally de-energized and being energized only when its respective output channel is energized by said sequential energizing means; first means for sequentially maintaining each of said output channels energized for a preselected length of time; second means for sequentially energizing each of said output channels within a period of time less than said preselected length of time each time said first means maintains one of said channels; each of said output channels includes an energizable indicator associated therewith; said indicator being energized when its respective output channel is maintained energized by said first means; and first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and corresponding reselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal whereby said preselected ones of said first group of transducers will be compared to their respective reference signals each time said second means sequentially energized each of said output channels within said period of time.
 44. The apparatus of claim 43 and further including ''''discontinuous scan'''' circuitry responsive to the occurrence of said first alarm signal for preventing said second means from energizing any further output channel than the one output channel which corresponds to the transducer the magnitude of whose output signal caused said first alarm signal.
 45. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; each of said output channels including primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of each of said channels being normally de-energized and being energized only when its respective output channel is energized by said sequential energizing means; first means for sequentially maintaining each of said output channels energized for a preselected length of time; second means for sequentially energizing each of said output channels within a period of time less than said preselected length of time each time said first means maintains one of said channels; a channel position counter which sequentially produces a higher numbered channel signal each time said channel position counter is pulsed by a channel position advance pulse which occurs once every preselected length of time; said second means includes a second counter for sequentially producing a higher numbered channel selection signal at a rate greater than the production of said channel clock position pulses; and further including coincidence comparator means for stopping said second counter whenever the numbered channel selection signal produced by said second counter equals the channel signal produced by said position counter.
 46. The apparatus of claim 45 wherein each of said signals produced by said plurality of transducers is an analog voltage signal the magnitude of which represents the instantaneous value of the respective parameter which said transducer is monitoring; wherein said display means includes analog to digital conversion means for converting said analog voltage signal to a corresponding digital signal as said analog signals are sequentially presented to said display means; wherein said display means first includes display bulb means responsive to said digital signal for visably displaying the decimal value of said digital signal; and further including pulse generator means for producing a repetitive initiation pulse which is applied to said analog-to-digital conversion means to initiate the conversion process; said A-D conversion means producing an end of conversion pulse each time said conversion process is complete; and further including main buffer storage means intermediate said A-D conversion means and said display bulb means for temporarily storing said digital signal and impressing same on said display bulb means; read pulse generating means for generating a repetitive read pulse at a predetermined interval of time; and enabling logic circuit means responsive to the simultaneous occurrance of one of said read pulses and one of said end of conversion pulses for enabling said main buffer storage means to receive and store said digital signal from said A-D conversion means; said read pulse generator means comprising said coincidence comparator means and said read pulse comprising a coincidence signal produced by said coincidence comparator means when said numbered channel selection signal equals the channel signal produced by said position counter.
 47. The apparatus of claim 46 and further including first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; and further including ''''discontinuous scan'''' circuitry responsive to the occurrence of said first alarm signal for preventing said second means from energizing any further output channel than the one output channel which corresponds to the transducer the magnitude of whose output signal caused said first alarm signal; and further including auxiliary read pulse generating means responsive to the occurrence of said first alarm signal for producing an auxiliary read pulse which, together with one of said end of conversion pulses, enables said enabling logic circuit means such that said main buffer storage means will receive and store the digital signal from said A-D conversion means which corresponds to the signal with which brought about said first alarm signal.
 48. The apparatus of claim 47 and further including alarm indicating means responsive to the occurrence of first alarm signal for providing an observable indication of the occurrence of said first alarm signal.
 49. The apparatus of claim 47 wherein said plurality of transducers are monitoring various variable parameters associated with the operation of a motor driven device; and further including motor disabling circuit means responsive to the occurrance of said first alarm signal for shutting down said motor.
 50. The apparatus of claim 49 and further including means to prevent the operation of said motor disabling circuit means should an operator desire to operate said motor even upon the occurrence of said first alarm signal.
 51. The apparatus of claim 74 wherein each of said signals produced by said plurality of transducers is an analog voltage signal the magnitude of which represents the instantaneous value of the respective parameter which said transducer is monitoring; wherein said display means includes analog to digital conversion means for converting said analog voltage signal to a corresponding digital signal as said analog signals are sequentially presented to said display means; wherein said display means first includes display bulb means responsive to said digital signal for visibly displaying the decimal value of said digital signal; and further including pulse generator means for producing a repetitive initiation pulse which is applied to said analog-to-digital conversion means to initiate the conversion process; said A-D conversion means producing an end of conversion pulse each time said conversion process is complete; and further including main buffer storage means intermediate said A-D conversion means and said display bulb means for temporarily storing said digital signal and impressing same on said display bulb means; read pulse generating means for generating a repetitive read pulse at a predetermined interval of time; and enabling logic circuit means responsive to the simultaneous occurrence of one of said read pulses and one of said end of conversion pulses for enabling said main buffer storage means to receive and store said digital signal from said A-D conversion means; said read pulse generator means comprising said coincidence comparator means and said read pulse comprising a coincidence signal produced by said coincidence comparator means when said numbered channel selection signal equals the channel signal produced by said position counter; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; and further including ''''discontinuous scan'''' circuitry responsive to the occurrence of said first alarm signal for preventing said second means from energizing any further output channel than the one output channel which corresponds to the transducer the magnitude of whose output signal caused said first alarm signal; and further including auxiliary read pulse generating means responsive to the occurrence of said first alarm signal for producing an auxiliary read pulse which together with one of said end of conversion pulses enables said enabling logic circuit means such that said main buffer storage means will receive and store the digital signal from said A-D conversion means which corresponds to the signal with which brought about said first alarm signal; reset means for removing said first alarm signal and for disabling said ''''discontinue scan'''' circuitry whereby said second means can continue to energize said output channels, said reset means removing said first alarm signal and disabling said ''''discontinue scan'''' circuitry regardless of whether the condition which causes said alarm has subsided or not; whereby all of said output channels will be scanned once again before the occurrence of a subsequent first alarm signal will activate said ''''discontinue scan'''' circuitry.
 52. Apparatus for monitoring and displaying the magnitude of a plurality of variable parameters, said apparatus comprising: a plurality of transducers each producing a signal representative of the magnitude of one of said variable parameters; display means responsive to any one of said signals for displaying the magnitude of the respective parameter which said signal represents; sequencing means for sequentially presenting each of said signals to said display means; a plurality of output channels at least equal in number to said plurality of transducers, each of said output channels corresponding to one of said transducers; wherein said sequencing means further includes sequential energizing means for sequentially energizing each of said output channels; each of said output channels including primary enabling means for enabling its corresponding transducer to pass its respective signal to said display means; said enabling means of each of said channels being normally de-energized and being energized only when its respective output chanNel is energized by said sequential energizing means; holding circuitry means for energizing any selected one of said output channels; said hold circuitry means includes a selector switch for each of said output channels, activation of a specified selector switch initiating the energization of the corresponding output channel; a pulse generator responsive to the activation of said specified selector switch for producing a scan-to-hold pulse; wherein said sequential energizing means includes: first means for sequentially maintaining one of said output channels energized for a preselected length of time; second means for sequentially energizing each of said output channels within a period of time less than said preselected length of time each time said first means energizes one of said channels; wherein each of said signals produced by said plurality of transducers is an analog voltage signal the magnitude of which represents the instantaneous value of the respective parameter which transducer is monitoring; wherein said display means includes analog to digital conversion means for converting said analog voltage signal to a corresponding digital signal as said analog signals are sequentially presented to said display means; wherein said display means first includes display bulb means responsive to said digital signal for visibly displaying the decimal value of said digital signal; and further including pulse generator means for producing a repetitive initiation pulse which is applied to said analog-to-digital conversion means to initiate the conversion process; said A-D conversion means producing an end of conversion pulse each time said conversion process is complete; and further including main buffer storage means intermediate said A-D conversion means and said display bulb means for temporarily storing said digital signal and impressing same on said display bulb means; read pulse generating means for generating a repetitive read pulse at a predetermined interval of time; enabling logic circuit means responsive to the simultaneous occurrence of one of said read pulses and one of said end of conversion pulses for enabling said main buffer storage means to receive and store said digital signal from said A-D conversion means; said read pulse generator means comprising said coincidence comparator means and said read pulse comprising coincidence signal produced by said coincidence comparator means when said numbered channel selection signal equals the channel signal produced by said first counter; said scan-to-hold pulse being applied to said first and second counters to reset them to one; said scan-to-hold pulse being further applied to scan-to-hold flip flop circuitry to apply advance pulses to said first and second counters simultaneously until said specified output channel is energized; first comparator means responsive to the signals produced by preselected ones of a first group of said transducers and to corresponding preselected reference signals for providing a first alarm signal when any one of said signals produced by said preselected ones of said first group of transducers exceeds its corresponding preselected reference signal; and further including disabling means responsive to the occurrence of said first alarm signal for preventing said advance pulses from being applied to said first and second counters once a channel which corresponds to a transducer the output of which caused said first alarm signal, has been energized.
 53. The apparatus of claim 52 wherein each of said signals produced by said plurality of transducers is an analog voltage signal the magnitude of which represents the instantaneous value of the respective parameter which said transducer is monitoring; wherein said display means includes analog to digital conversion means for converting said analog voltage signal to a corresponding digital signal as said analog signals are sequentiAlly presented to said display means; and wherein said display means includes display bulb means responsive to said digital signal for visably displaying the decimal value of said digital signal; and further including pulse generator means for producing a repetitive initiation pulse which is applied to said analog-to-digital conversion means to initiate the conversion process; said A-D conversion means producing an end of conversion pulse each time said conversion process is complete; and further including: main buffer storage means intermediate said A-D conversion means and said display bulb means for temporarily storing said digital signal and impressing same on said display bulb means; read pulse generating means for generating a repetitive read pulse at a predetermined interval of time; enabling logic circuit means responsive to the simultaneous occurrance of one of said read pulses and one of said end of conversion pulses for enabling said main buffer storage means to receive and store said digital signal from said A-D conversion means; and further including additional read pulse generating means for producing a read pulse in the event said disabling means is energized. 